A secondary battery, which is easily applicable to various kinds of products and which exhibits excellent electrical properties, such as high energy density, is widely used in an electric vehicle (EV) or a hybrid electric vehicle (HEV), which is driven using an electrical driving source, as well as portable devices. Such a secondary battery has attracted considerable attention as a new energy source that is eco-friendly and exhibits high energy efficiency, since the secondary battery can remarkably reduce the use of fossil fuels and produces no by-products when energy is used.
Examples of the secondary battery that have been widely used to date include a lithium ion battery, a lithium polymer battery, a nickel cadmium battery, a nickel hydride battery, and a nickel zinc battery. The operating voltage of such a unit secondary battery cell is about 2.5 V to 4.2 V. In the case in which voltage higher than the above-mentioned voltage is required, therefore, a plurality of secondary battery cells may be connected to each other in series in order to constitute a battery pack. In addition, a plurality of secondary battery cells may be connected to each other in parallel in order to constitute a battery pack having required charge and discharge capacities. Consequently, the number of secondary battery cells included in the battery pack may be variously set depending on the required output voltage or required charge and discharge capacities.
Meanwhile, middle- or large-sized devices, such as vehicles, use a battery module including a plurality of battery cells electrically connected to each other or a middle- or large-sized battery pack including a plurality of battery modules as unit modules, because high output and large capacity are necessary for such middle- or large-sized devices. In general, a battery module is manufactured by stacking a plurality of battery cells with high integration. A large amount of heat is generated from the battery cells, which constitute the battery module, during the charge and discharge of the battery cells. If the heat generated from the battery cells during the charge and discharge of the battery cells is not effectively removed from the battery cells, the heat accumulates in the battery cells, with the result that deterioration of the battery cells is accelerated. Depending on the circumstances, the battery cells may catch fire or explode.
For this reason, a high-output, large-capacity battery module or a high-output, large-capacity battery pack needs a cooling system for cooling battery cells mounted in the battery module or the battery pack.
Korean Patent Application Publication No. 2015-0100529 discloses a battery pack for automobiles having improved cooling efficiency. In this related art document, the battery pack for automobiles includes at least one secondary battery, including a negative electrode plate, a separator, and a positive electrode plate, and at least one cooling fin disposed so as to contact an outer case of the secondary battery for cooling the secondary battery, characterized in that at least one end of the cooling fin is disposed so as to contact the body of an automobile, whereby no additional coolant, coolant channel, or pump is needed.
However, it is very difficult to apply the cooling structure disclosed in the related art document to a cylindrical battery cell, since the cooling structure is configured such that a planar cooling fin is interposed between secondary batteries having an approximately hexahedral structure so as to be adjacent to the secondary batteries and the cooling fin dissipates heat generated from the secondary batteries.